History of Related Art
Shaping the ground-plane of a wireless communication device (such as for instance a mobile phone, a smart phone, a PDA, an MP3 player, headset, USB dongle, laptop, PCMCIA or Cardbus 32 card) has been shown to be a useful technique to improve the radiation characteristics of such a device. This has been for instance disclosed in WO 03 023900. In several examples of the prior-art, at least a portion of such a shaped ground-plane includes a slot separating totally or partially at least two conducting regions on said ground-plane. Further there are several known antenna systems for wireless devices where the radiating antenna element is just a slot provided in the wireless device's ground plane. Usually such a ground-plane is embedded in a multilayer printed circuit board (PCB) which hosts the electronics and other components (for instance integrated circuits, batteries, handset-camera and speakers, LCD screens, vibrators) of the whole device. In these cases, the desired shape for the ground-plane can be cost effectively implemented by using conventional PCB manufacturing techniques.
One of the problems of placing the slot on such a PCB is to make the fine tuning of the frequency response of such a slot, and generally the whole ground-plane. Although several electromagnetic CAD tools can approximately model the response of the geometry, usually the final design is tuned experimentally. This involves an iterative process where several PCBs are to be prototyped and produced before closing the final PCB design. This is a costly process, which in turn might delay the commercial launching of the project.
On the other hand, embedding a slot in the ground-plane some times is difficult due to the size of the slot and space constrains. If a multiband response of the slot is desired, then usually the shape of the slot involves several branches with several characteristic lengths that can fit the multiple wavelengths. In this later case, again the space is a constraint that can make the solution impractical or unfeasible.